1. Field of the Invention
The present invention-relates to an interpolation frame generation device, and more particularly to an interpolation frame generation device for generating an interpolation frame for interpolating image frames. The present invention further relates to a method for generating an interpolation frame and a program for generating an interpolation frame.
2. Description of the Prior Art
An interpolation technique for a television set, a personal computer (PC), a cellular phone or other devices that display an image signal, in which an interpolation frame for interpolating image frames is generated from image frames that form the image signal, and the generated interpolation frame is inserted between the image frames to be displayed, is well known in the prior art. This technique is used to smoothly display an image signal that is transmitted at a low frame rate in order to reduce the volume of the data, for example.
FIG. 52 shows an interpolation frame generation device 401 for effectuating the above-mentioned conventional technique. The interpolation frame generation device 401 comprises a frame memory 402, a motion vector detecting unit 403, an interpolation frame generating unit 404, a signal switching unit 405 and a control unit 406. The frame memory 402 stores an input image signal 410 for each image frame. The motion vector detecting unit 403 detects a motion vector between a base frame and a reference frame that are two image frames stored in the frame memory 402. More specifically, the motion vectors of image blocks forming the base frame are detected by matching the image blocks of the base frame with a pixel area of the reference frame. The interpolation frame generating unit 404 generates an interpolation frame from the base frame and detected motion vectors of the image blocks of the base frame. The signal switching unit 405 switches between the image frame stored in the frame memory 402 and the interpolation frame generated by the interpolation frame generating unit 404 so as to provide an output image signal 411. The control unit 406 provides control signals necessary for operating the motion vector detecting unit 403, the interpolation frame generating unit 404 and the signal switching unit 405.
Here, with reference to FIG. 53, the operation of the motion vector detecting unit 403 and the interpolation frame generating unit 404 will be described in more detail. FIG. 53A shows a base frame BF415 and a reference frame RF416 stored in the frame memory 402. Here, a situation will be described in which one interpolation frame CF417 is inserted between the base frame BF415 and the reference frame RF416 (see FIG. 53B). The motion vector detecting unit 403 divides the base frame BF415 into image blocks each of which includes a predetermined number of pixels. In addition, each of the divided image blocks is matched with a pixel area that forms the reference frame RF416 in order to detect a motion vector MV420. The interpolation frame generating unit 404 performs internal division of the detected motion vector MV420 in accordance with the number of interpolation frames. Here, one interpolation frame CF417 is inserted between the base frame BF415 and the reference frame RF416, so the size of the motion vector MV420 is transformed into half without changing the direction of the same so as to derive an interpolation motion vector CMV421. The derived interpolation motion vector CMV421 and the image block of the base frame BF415 are used for generating the interpolation frame CF417.
Furthermore, another technique well known in the prior art is one in which not only the motion vector for the reference frame RF416 of the image block of the base frame BF415, but also the motion vector for the base frame BF415 of the image block forming the reference frame RF416 is detected, in order to generate the interpolation frame CF417 (see Japanese unexamined patent publication No. 6-178270) or to improve the accuracy with which the motion vector is detected (see Japanese unexamined patent publication No. 2000-134585).
On the other hand, there are demands to further improve the accuracy of interpolation frame generation so that an image signal transmitted at a low frame rate in order to reduce data volume will be displayed smoothly. There are also demands to decrease the volume of calculation or the size of the circuit when enabling the technique for generating an interpolation frame in a device.